Copper oxide rectifier



overlying layer of cupric oxide.

Patented Feb. 29, 1944 COPPER RECTIFIER o." c. nein, Forest nun, Pit, assignor to Westinghouse Electric it Manufacturing Company. East Pittsburgh, Pa., a corporation of Pennsylvania Application August 2:, 1941, Serial No. 408,05)

8 Claims.

My invention relates to copper oxide rectifiers and, in particular, relates to methods of heat treating such rectifiers to render their electrical characteristics less liable to variation with time.

One object of my invention is to provide a method of manufacturing copper oxide rectifiers which shall make it possible to operate them with a higher direct-current wattage output than has been possible with copper oxide rectifiers of the prior art.

Another object of my invention is to provid a method of manufacturing copper oxide rectifiers which shall decrease the tendency of rectifier disks of a given size when operated at arelatively high wattage output to vary in internal electrical resistance in the course of'continued use.

Another object of my invention is to provide a method of manufacturing copper oxide rectifiers which shall render their electrical characteristics less subject to change with time when operating at comparatively elevated temperatures.

Other objects of my invention will become apparent upon reading the following specification, taken in connection with the drawing in which the single figure is a diagram illustrating the variation of internal resistance in the conductive direction at a fixed current with passage of time for rectifier disks manufactured by two difierent methods, the rectifiers being maintained at an artificially elevated'temperature.

Copper oxide rectifiers may, in accordance with and sets a serious limitation on the wattage of the direct-current output which they can supply. It

the temperature of the disks is allowed to rise toohigh, they will, in fact, undergo an electrical breakdown and be mined. To take care of this situation, various means of dissipating heat from the rectifier disks are used, and the wattage output which they can supply is limited by the amount of heat which can be dissipated without the disclosure of'Grondahl Patent No. 1,640,335,

be manufactured by oxidizing plates of copper in air at a temperature not far below the melting point of the "copper, cooling the oxidized disks to room temperature and removing the As is described in Geiger Patent No. 1,892,832, the oxidized copper may be transferred whil just below its melting point to'an air-filled furnace, heated to about 600 C. and'allowed to cool to near the latter temperature;' thereafter being plunged into a tank of cold water.

' It is found that when copper oxide disks manufactured in the way'last mentioned and made up into rectifiers of the form described in the Grond'ahl and Geiger patents are operated to supply such a rise in their'temperature that there is a danger of their undergoing breakdown.

It has been found that the rate of increase of resistance of the rectifier disks gradually decreases with time, and that the more rapid increase found during the earlier days or weeks of the rectifier operation Gan be accelerated by operating the rectiflers in an environment of artificially elevated temperature; for example, at a temperature of 0. However temperatures up to C. may be desirable for certain conditions of use; and temperatures of 80 C. and even below that down to room temperature are still effective in'others. In this way. the greater part of the change of internal resistance can be caused to take place within a comparatively short time the lapse of time in days and the ordinates 1 represent the intemal'resistance of the rectifier in percent of its initial resistance.

My application, Serial No. 286,613, for Copper oxide rectifiers, filed July 26, 1939, and assigned to the Westinghouse Electric 8: Manufacturing Company of East Pittsburgh, Pennsylvania, describes a novel method of manufacturing copper oxide rectifier disks which is an improvement on the methods described inthe Grondahl and Geiger patents above mentioned. In accordance with my above-mentioned application, the copper blanks before oxidation are heated to a temperature between 500 C. and the fusing point of copperin a vacuum; for one example, a pressure of the order of 30 microns. It is preferable thatv this heating should continue for a substantial time interval; for example periods up to three hours have been found useful, although periods of a few minutes'are eflective for many typesof unit.

when copper oxide rectlfiers are given this vacuum pre-treatment and subsequently oxidized in accordance with the description in the Geiger patent, I have found that the resistance in the conductive direction through the rectifier decreases very materially and that the resistance in the non-conductive direction through the rectifier substantially increases: and that the rectifier can furnish direct-current outputs of from six to eight times as great in watts as rectifiers made by the prior art methods. I have also found that the characteristics of the rectifiers made by my above-mentioned vacuum treatment to be otherwise substantially difierent from those of rectifiers made by the prior art methods.

Experiments with my vacumn pre-treated rectillers have further shown that operation in 'an' artificially increased ambient temperature of the order of 80 C. causes their internal resistance to increase to a substantial maximum value in the course of a few days and to thereafter remain comparatively constant for long periods of time.

The final increase of resistance in my vacuinn pre-treated disks is likewise a smaller percentage of their initial resistance than is the increase of resistance of rectifiers made in accordance with the prior'art. This is illustrated by the curveB in the drawing which shows the increase of internal resistance of rectifiers made in accordance with my vacuum pro-treatment process in the course of time plotted to the same scale as the. curve A already mentioned.

As a result of the greater stability in respect to internal resistance of my vacuum pre-treated rectifiers, it is possible to operate them for long periods of time at a higher wattage of directcurrent output than is possible with the case of rectifiers made by the methods of the prior art. For example, a rectifier having an output of 26 volts at one ampere, corresponding to 26 watts output, was obtained on disks made in accordance with my above-mentioned vacuum pretreatment method, whereas a rectifier of the same size made by methods of the prior art yielded only 9 volts at one-half an ampere, corresponding to 4 watts output. Thus my imroved rectifier gives an output nearly six times as great as that possible with those of the prior art.

I have further found that the electrical efilciency of my above-mentioned vacuum pre-treatment rectifier is much more constant than that of the prior art rectifiers, being substantially invariable after the first ten days of its operation.

I claim as my invention:

1. The method of manufacturing copperoxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the melting point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature and maintaining it at a temperatureof the order of 100 C. for an extended period.

2. The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the melting'point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature and maintaining it at a temperature of the order of 100 C. for a period of the order of days in duration.

3. The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500' C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the melting point of copper in an atmosphere contalning oxygen,-cooling said blank to .a tempera.- ture of the order of room temperature, removing any cupric oxide present from the surface of said blank, providing electrical contacts to the'mother ing said blank at a temperature up to the melting point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature, removing any cupric oxide present from the surface of said blank, providing electrical contacts to the mother metal of the blank and to the outer surface of the cuprous oxide layer, and raising the unit thus produced to a temperature of the order of C. and maintaining it at the last-mentioned temperature for a period of the order of days in duration.

5. The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the melting point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature and maintaining it at a temperature up to about C. for an extended period.

6; The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the'melting point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature and maintaining it at a temperature up to about 140 C. for a period of the order of days in duration.

7. The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing said blank at a temperature up to the melting point of copper in an atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature, removing any cupric oxide present from the surface of said blank, providing electrical contacts to the mother metal of the blank and to the outer surface of the cupric oxide layer, and raising the unit thus produced to a temperature up to about 140 C. and maintaining it at the last-mentioned-temperature for a long time. a

8. The method of manufacturing copper oxide rectifiers which comprises heating a copper blank for a substantial time interval at a vacuum pressure at a temperature between 500 C. and the fusing temperature of copper, thereafter oxidizing saidblank at a temperature up to the melting point of copper in an' atmosphere containing oxygen, cooling said blank to a temperature of the order of room temperature, removing any cupric oxide present from the surface of said blank, providing electrical contacts to the mother metal of the blank and to the outer surface of the cuprous oxide layer, and raising the unit thus produced to a temperature up to about 140 C, and maintaining it at the last-mentioned temperature for a period of the order of days in duration.

CARL C. HEIN. 

